The present invention relates to methods and apparatus for modifying a patient's femur in order to prepare same for receiving a patellofemoral knee arthroplasty.
The patellofemoral joint of the knee is an articulating joint between the patella and the femur. This joint includes an articular surface on the posterior of the patella and a corresponding articular surface on the anterior distal portion of the femur, also termed the trochlear groove. The posterior of the patella is contoured as a ridge, while the trochlea is contoured as a groove that is dimensioned to receive the patellar ridge in a complementary manner. Proper dynamic function of the patellofemoral joint requires that the patellar ridge accurately track the underlying trochlear groove when the knee is moved through flexion or extension.
Joint disorders arise with varying severity, pain and dysfunction. Some less severe, disorders involve minimal or no errors in patellar tracking of the trochlear groove. Other more serious disorders are characterized by patellar misalignment, transient displacement, or dislocation (such as permanent displacement, of the patella from the trochlear groove).
During functional movement of the knee joint, various tracking errors can occur due to injury, overuse, or changes inherent to adolescent growth, which in each case causes pain and dysfunction. When the patella is seated in the trochlear groove at a range greater than about 60 degrees of knee flexion, there is very little movement of the patella outside of the trochlear groove. Between about 0-40 degrees of knee flexion, and especially about 20-40 degrees, however, there is a propensity for the patella to track away from the groove as the knee flexes.
Rehabilitation of the weakened joint is often limited to the extent that correct tracking is absent, or ineffectively applied, and the resulting pain makes exercise too unbearable. As the quadriceps contract, they apply a lever force to the patellofemoral joint that is substantially directly related to the overall patellofemoral joint stress. Pain associated with such stress increases in relation to the amount of overall stress. Accordingly, as the quadriceps contract more powerfully, such as while going up stairs or doing squats, overall stress and associated pain increases.
In addition, patellofemoral joint stress at any given contact area increases as the overall patellofemoral joint stress is focused about a smaller patellofemoral contact surface area. Pain associated with such stress increases in direct relation to a reduction in the amount of patella-to-femur contact surface area. Thus, patellofemoral pain is not only directly related to the overall joint force applied between the patella and the femur, it is inversely related to the amount of patellofemoral contact surface area. Rehabilitation of the weakened joint through quadriceps contraction is therefore limited by the pain associated with both overall patellofemoral joint stress and a minimal patellofemoral contact surface area.
Joint arthroplasty is a surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. Patellofemoral arthroplasty is a type of joint arthroplasty wherein the anterior compartment of a patient's knee, or portion thereof, is replaced with one or more prosthetic components. Additionally, in some cases, the patient's patella may be replaced by an orthopedic prosthesis. Typical patellofemoral arthroplasty procedures may include replacing a patient's femoral trochlea, and in some cases, one or both femoral condyles with prosthetic components. Typical orthopedic surgical procedures require the entire anterior femur to be resectioned to allow overlay of the prosthetic joint components. However, the prosthetic joint components may not replace the entire volume of resectioned bone. Additionally, many patellofemoral arthroplasty procedures and instrumentation reference off of the intramedullary canal of the patient's femur, which resultantly compromises the intramedullary canal.
Different methods and apparatus have been developed in the past to enable a surgeon to remove bony material to create specifically shaped surfaces in or on a bone for various reasons, including to allow for attachment of various devices or objects to the bone. Keeping in mind that the ultimate goal of any surgical procedure is to restore the body to normal function, it is important that the quality and orientation of the cut, as well as the quality of fixation, and the location of the component(s) of the prosthesis are all sufficient. It has been said that a “well placed, but poorly designed implant will perform well clinically, while a poorly placed, well designed implant will perform poorly clinically.”
Unfortunately, the conventional methods and apparatus for preparing the femur for a patellofemoral prosthesis result too often in misalignments and/or poor fit between the prepared anterior and distal portions of the femur and the prosthesis. Clinical results, therefore, suffer.
In view of the above, there are needs in the art for new methods and apparatus for preparing a patient's femur in order to receive a patellofemoral knee prosthesis. Among the desired characteristics of such new methods and apparatus are the ability to yield a modified anterior and/or distal femur that exhibits tightly controlled cuts in order to achieve repeatable, accurate, and precise alignment and fit of the prosthesis to the femur.